1. Field of the Invention
The present invention relates to a power transmission for motor vehicles, and more particularly to a power transmission suitable for use in a four-wheel drive vehicle, which transmission is equipped with an ancillary change-speed mechanism for providing an extra-low-speed gear train the reduction gear ratio of which is larger than that of a first-speed gear train in a main change-speed mechanism.
2. Description of the Prior Art
In Japanese Patent Early Publication No. 59-133850, there has been proposed a power transmission as described above, which transmission comprises a main change-speed mechanism including an input shaft drivingly connected to a crankshaft of a prime mover of the vehicle, an output shaft arranged in parallel with the input shaft, and a plurality of change-speed gear trains provided on the input and output shafts to transmit the power from the input shaft to the output shaft at a selected reduction gear ratio, and an ancillary change-speed mechanism for providing an extra-low-speed gear train the reduction gear ratio of which is larger than that of the first-speed gear train in the main change-speed mechanism. The ancillary change-speed mechanism comprises a pair of ancillary shafts arranged in parallel with the input shaft, first and second idler gears each mounted on one of the ancillary shafts for rotation therewith, the first idler gear being in mesh (i.e. in Meshing engagement) with a drive gear on the input shaft, a third gear axially slidably mounted on the other ancillary shaft, a fourth gear mounted on the output shaft for rotation therewith, and clutch means arranged to shift the third gear for meshing engagement with the second idler gear and the fourth gear. In the power transmission, it is advantageous that the ancillary change-speed mechanism is arranged in parallel with the main change-speed mechanism without causing any increase in axial length of the power transmission. It is, however, disadvantageous that the ancillary change-speed mechanism is complicated in construction and of relatively large width due to the provision of such additional component parts as described above.